These investigations will be concerned with the role of several proteins in the motile processes of cell division and early development, using as experimental material the synchronously dividing eggs of the sea urchin. A highly structured polymer of actin and a second protein of 58,000 MW has been induced in cell extracts and its molecular organization is now being determined. The possible roles of this polymer in cell motility, chromosome movement and cytokinesis will be investigated. These studies will be carried out primarily through the isolation of the cell organelles involved, such as the mitotic apparatus and cell cortex and the subsequent determination of their protein composition and structure. The possible involvement of actin in the mitotic apparatus is of particular interest as it may be an example of the collaboration of actin and microtubules in a motile process. The role of the protein hyalin, the basic component of the hyaline layer of the embryo will also be investigated. This material is released by the breakdown of the cortical granules at fertilization and act to hold the blastomeres of the embryo together during development. Changes in the properties of this material have been observed during development and these will be related to chemical changes in the protein hyalin. The significance of these changes in relation to the possible role of this material in cell division and in cell aggregation will be investigated.